Energy harvesting devices and systems are getting more and more attention as the demand for green energy is increasing. This means that devices, like thermoelectric (TE) devices, that can convert waste heat from electrical equipment into electricity are becoming more and more important.

Dr Lijie Li, College of Engineering at Swansea University and Dr Jian-Hua Jiang at Soochow University, China have been studying how new technology can be used in thermoelectric devices to improve their performances. Their research has been published recently in the prestigious journal – Scientific Reports (Nature Publishing Group).

The main challenge in thermoelectric (TE) is how to improve the Seebeck* coefficient, which determines ultimately the power factor. Three-terminal TE overcomes the disadvantage caused by the identical heat flow path and electrons flow path. However the material used in three-terminal TE still requires careful selection in order to minimize leakage due to transverse heat flow. Sometimes this type of leakage is unavoidable for any electrically conducting materials; moreover it is difficult to precisely predict the performance theoretically.

Dr Lijie Li and Dr Jian-Hua Jiang have proposed a new configuration for the three-terminal TE in which serially connected quantum dots with staircase energy levels is used to optimize the power factor. The device can operate at room temperature or above.

With this concept, the power factor can have a maximal value at the condition of an optimal number of quantum dots (the energy step between adjacent two dots is fixed), at which the highest output power can be achieved. The heat leakage will be reduced significantly as the lateral/transverse electrical conductivity is much lower than the axial electrical conductivity. The physics of the new configuration has been explained and full analysis has been conducted to validate this concept. It is so far the only configuration that can generate the maximum output power of this kind of the devices. The realization of the concept has also been discussed such as embedding a series of quantum dots inside nanowires.